The present invention relates to the technical field of gas turbines. It relates to a rotor for a gas turbine, which rotor comprises a plurality of rotor disks arranged one behind the other in a rotor axis and connected, in particular welded, to one another, and which rotor extends between a compressor part and a turbine part and has a central bore running between both parts and having an inside diameter, there being first means which branch off cooling air in the compressor part and direct it radially inward through the rotor into the central bore, and there being second means which, in the turbine part, direct the cooling air from the central bore radially outward through the rotor.
Guidance of the cooling-air flow via the central bore in the rotor has been disclosed, for example, by U.S. Pat. No. 5,271,711.
Widely varying requirements are imposed on the rotors of gas turbines. In particular, the rotors are to be designed in such a way that cooling-air mass flows can be extracted at the compressor and directed with low losses through the central bore of the rotor to the (low-pressure) turbine in order to cool the moving blades there. In this case, the rotor is at the same time also to be capable of being produced by welding together from individual disks and is to be cost-effective to produce overall.
In order to keep down the flow losses, a situation must be avoided in which swirl flows can develop in the cooling-air flow. For that reason, the cooling air must be directed on its radial path to and from the central bore. Suitable bores for this in terms of production are radial bores. However, large cooling-air mass flows require large cross sections of the bores, so that the bores, in the required number and size, already converge at a diameter which is markedly above the inside diameter of the central bore.
A further possible solution is (radial) ribs which subdivide the cavities between the disks of the rotor into smaller chambers and thus prevent the swirl formation in the cooling-air mass flow. However, such ribs are expensive to produce and are highly stressed mechanically by the forces occurring at the high speeds of the rotor. In the case of welded rotors, there is also the further restriction that these rotors can only be repaired with great difficulty, i.e. welded rotors must be designed in such a way that crack formation can be ruled out.
The known solutions meet only some of the abovementioned requirements. The disks are partly designed as components of bolted rotors. This joining technique permits more degrees of freedom in the geometry of the disks, so that the ribs referred to can be realized more-easily. In addition, a bolted rotor can be repaired. In welded rotors, this is therefore not the case. However, the disks are also partly designed for smaller cooling-air mass flows. In this case, the cooling-air bores can be run almost directly up to the central bore without overlapping occurring.
A solution which equally meets all requirements is not known.
It is therefore the object of the invention to provide a rotor for a gas turbine which avoids the disadvantages of known rotors and in particular enables large cooling-air mass flows to be directed with low losses with at the same time high mechanical stability.
The essence of the invention consists in combining radial bores and a cavity subdivided by ribs with one another in such a way that, on the one hand, a large total cross section for the cooling air is achieved with the bores and, on the other hand, the ribs are only subjected to a comparatively moderate centrifugal force. In the outer rotor region subjected to the greatest stress by the centrifugal forces, the air is extracted through radial bores. The end of the bores is shifted in the direction of the rotor axis to such an extent that the discharge openings are at an acceptable distance from one another. The cavity into which the bores open, and into which the cooling air is then injected, is subdivided into chambers by relatively short ribs which prevent a build-up of swirl. These short ribs have the advantage that they end on a relatively small outer radius of the cavity, and thus the loading centrifugal forces are kept small.
In principle, the bores may have different diameters and be at a distance from one another which may at first be any desired distance and is selected in such a way that the requirements with regard to strength, producibility and aerodynamics are met. However, a first preferred embodiment of the rotor according to the invention is characterized in that all the first radial bores have the same bore diameter, and in that the outside diameter of the first cavity is selected in such a way that the distance between two adjacent first radial bores at the orifice to the first cavity corresponds approximately to the bore diameter. An optimized compromise between mass flow and rib stress is achieved by this dimensioning.
A further improvement in the strength of the ribs is obtained if, according to a second preferred embodiment of the invention, the first ribs converge in the center of the first cavity in a common hub.
The production becomes especially simple if, according to another preferred embodiment of the rotor according to the invention, the first cavity and the first ribs located therein are fashioned out of the first rotor disk by milling out from one side, and the first cavity is defined by an adjacent rotor disk.
Depending on the guidance of the cooling-air mass flow, the first radial bores may run in a plane perpendicular to the rotor axis or may be positioned in the axial direction. For fluidic reasons, however, it may also be advantageous if the first radial bores are positioned in the tangential direction.